1. Field of the Invention
The present invention relates to a toroidal-type continuously variable transmission and a continuously variable transmission apparatus for use in a power transmission system of a vehicle.
2. Description of the Related Art
Conventionally, in a power transmission system of a vehicle, there is used a toroidal-type continuously variable transmission of a double cavity type. The toroidal-type continuously variable transmission of a double cavity type, for example, as disclosed in JP-A-2000-9196 or in Japanese Patent No. 2629786, includes a pair of input disks, a pair of output disks, a plurality of power rollers, a pressing device and an output gear.
The pair of input disks are disposed in such a manner as to be spaced from each other in the axial direction of an input shaft. The pair of output disks are interposed between the two input disks and opposed to their associated input disks. The plurality of power rollers are interposed between the mutually opposed input and output disks. The pressing device presses the input disk toward the output disk. The output gear rotates integrally with the output disks.
Further, there has been developed a continuously variable transmission apparatus which is a combination of a toroidal-type continuously variable transmission using a loading cam with a planetary gear mechanism. For example, there is known a continuously variable transmission apparatus, in which a toroidal-type continuously variable transmission and a planetary gear mechanism are disposed substantially concentrically with an engine shaft, and power is circulated between the input shaft and the output gear of the toroidal-type continuously variable transmission. And, the planetary gear mechanism includes a clutch capable of switching a low speed mode, a high speed mod, and a retreating mode over one another.
In this type of continuously variable transmission apparatus, for example, as shown in DE19821417A1, in order to prevent a pressing force by the loading cam from increasing excessively, a hollow shaft is disposed on the outer periphery side of the input shaft in such a manner as to be concentric with the input shaft, and first and second input disks are connected to each other by the hollow shaft, whereby torque transmitted from the input shaft can be distributed to the pair of input disks.
In a toroidal-type continuously variable transmission, it is important to supply a sufficient quantity of lubricating oil to the portions of the toroidal-type continuously variable transmission to be lubricated, for example, bearings and ball splines. For example, as disclosed in JP-A-2000-9196, in order to lubricate bearings or ball splines for supporting disks or gears, an oil passage is formed in the interior of an input shaft, and a hole which communicates with the oil passage is opened up in the vicinity of the bearings or ball splines.
However, the above described toroidal-type continuously variable transmission structured such that the input shaft penetrates through the hollow shaft restricts the outside diameter of the penetrating portion of the input shaft, where the input shaft penetrates through the hollow shaft. Therefore, there arises a problem that, when an oil hole is formed in the input shaft, there occurs an excessive stress in the periphery of the oil hole. In order to lower the level of the stress, it is effective to increase the sizes of the parts of the toroidal-type continuously variable transmission. However, this raises another problem that the whole size of the toroidal-type continuously variable transmission is increased and thus the weight thereof is also increased.
Especially, a tensile load from the loading cam and a torsional load due to the engine torque are applied to the input shaft at the same time. Also, since stresses concentrate in the vicinity of the oil hole, there is generated an excessive stress. In particular, in the portion where the input shaft penetrates through the hollow shaft, the outside diameter of the input shaft is limited according to the inside diameter of the hollow shaft and thus the shaft diameter thereof is reduced, thereby raising the level of the stress. This makes it more difficult to form an oil hole in the input shaft. Even in case where the hardness of the periphery of the oil hole was increased by heat treatment, the strength of the oil hole could not be increased so much due to the existence of an abnormal layer caused by heat treatment.
By the way, as disclosed in Japanese Patent No. 2629786, there is proposed a structure that a clearance between the input shaft and hollow shaft is used as a lubricating oil passage. However, in this structure, of the whole length of the input shaft, the oil hole is formed in the portion (the portion where the shaft diameter is small) of the input shaft that penetrates through the hollow shaft; and, therefore, there is a possibility that the input shaft can be damaged by the excessive stress concentration.